The present invention relates to a lifting device. More particularly, the present invention relates to a lifting device capable of calculating the center of gravity of a load and determining if the center of gravity exceeds safety parameters.
In fork lifts, the tipping moment is critical to machine safety. In fork-lift trucks, the center of gravity of the lifted load is naturally outside the wheel contact surface. The amount of counterweight is sized based on factors such as wheel base, lifting capacity, and distance from the center of the front axle to the center of the load.
In some applications, the operator has a limited knowledge of either the weight of the lifted load, the center of gravity of the load, or both. If an operator lifts a load that has a weight within the lifting capacity of the machine, but the center of gravity is too far out front, the machine risks tipping forward. If the center of gravity of the load is within the machine rating, but the weight lifted is too great, the machine risks tipping forward. The product of the load weight times the distance to the load center is known as the load moment. The operator needs to know if the load moment is within the safe limits of the machine.
In other lifting systems, such as cranes, there are many techniques used to provide an operator information on the safe lifting of various loads. In most fork lift applications, if the load weight varies or is not known, a scale is added to the machine such that the load weight can be measured and displayed. The shape of the load is typically of a sort that an operator can easily measure or evaluate the load center of gravity location. Thus, in most fork lift applications, the operator can determine the safety of lifting various loads.
Prior attempts have been made to address the issue of tilt and center of gravity. For example, Rickers et al., U.S. Pat. No. 6,385,518, discloses an industrial truck, such as a fork-lift, that detects a tilt of the industrial truck based on wheel load. Wheel load sensors are used to detect a load moment of the fork-lift and then signal an alarm if tilt is detected. However, the condition of the wheels themselves may affect the ability of the wheel load sensors to properly detect load moment. In another example, Goto, U.S. Pat. No. 6,425,728, discloses a tilt speed control system that controls the tilt speed of a fork-lift mast, based on the weight of a load and lift height of the load as the load is being lifted. However, this system fails to assist the user in determining if the load is causing the lift to exceed safety limits. In a further example, Bruns, U.S. Pat. No. 5,666,295, discloses dynamic weighing of loads in hydraulically operated lifts. However, Bruns only discloses determining the weight of a load and fails to assist the user in determining if the load is causing the lift to exceed safety limits.
In a few applications, even if the operator knew the weight of the load, there still might be considerable difficulty in determining the location of the center of gravity. An example is that-of lifting boats. Engine location, amount and location of ballast, amount of fluid in the water and fuel tanks, all can be extremely difficult for the operator to determine or evaluate. There is a need to know what the load moment is as the forks engage the boat hull.
While methods such as those described above may provide a means for tilt caused by a load on a lift, such methods can always be improved.
Accordingly, there is a need for a means to measure both load weight and load moment as the load is engaged on the lifting machine. Further, there is a need to provide information to the operator about the weight and location of the center of gravity, provide a warning if the load is near the rated capacity of the machine, and disable the lifting capability if there is a danger of tipping. The present invention fulfills these needs and provides other related advantages.
The present invention resides in a process and system for a lifting determining an actual load moment, weight, and location of the center of gravity of a weighted load on a lifting machine and determining if the safety parameters of the machine are exceeded.
The invention provides a means to measure both load weight and load moment as the load is engaged on the lifting machine, provide information to the operator about the weight and location of the center of gravity, provide a warning if the load is near the rated capacity of the machine, and disable the lifting capability if there is a danger of tipping.
In accordance with a preferred embodiment of the present invention, a process for monitoring load conditions on a lifting machine having a rated load moment includes determining an actual load moment of the lifting machine due a weighted load. The actual load moment may be determined by measuring a tilt pressure within a hydraulic tilt cylinder of the lifting machine, and then calculating the actual load moment from the tilt pressure within the hydraulic tilt cylinder.
The process also includes determining a location of a center of gravity of the weighted load. This is determined by measuring a lift pressure within a hydraulic lift cylinder of the lifting machine, and then calculating the weight of the weighted load from the lift pressure. Once the weight is determined, the location of the center of gravity of the weighted load may be found using the actual load moment and the calculated weight.
Information about the weight and the location of the center of gravity of the weighted load may be also provided to a user. Warnings may be provided to the user if the weighted load is near the rated load moment of the lifting machine. A first warning may be activated if the actual load moment is below a first predetermined load moment. Second and third warnings may be activated, respectively if the actual load moment is above the first predetermined load moment and below a second predetermined load moment, or if the actual load moment is above the second predetermined load moment.
The first, second, and third warnings may be in the form of colored lights. The first and second predetermined load moments may be, respectively, between 80% to 100% of the rated load moment and 100% to 120% of the rated load moment. Additionally, an audio alarm may be engaged, respectively, if the actual load moment is above the first predetermined load moment and below the second predetermined load moment or if the actual load moment is above the second predetermined load moment.
If a load pressure switch of the lifting machine is activated, the hydraulic lift will be disabled.
Further in accordance with the present invention, a hydraulic stabilizer system may be configured as a hydraulic lift having a rated load moment. The system includes a means for measuring pressure within the hydraulic lift and a processor for determining an actual load moment of the hydraulic lift and for determining a weight of a load on the hydraulic lift based on pressure within the hydraulic lift.
The system also includes an illuminated display for warning an operator of the hydraulic lift if at least one predetermined operating parameter is exceeded; and a load pressure switch for disabling the hydraulic lift if another predetermined operating parameter is exceeded.
The hydraulic lift includes a frame, at least one load bearing member operationally connected to the frame for movement relative thereto. The lift also includes a hollow lift cylinder housing a lift piston and hydraulic fluid and a hollow tilt cylinder housing a tilt piston and hydraulic fluid. Each cylinder piston is operationally connected to the load bearing member, with the hydraulic fluid disposed between the piston and one end of the frame. The lift piston imparts a lift force upon the hydraulic fluid within the lift cylinder proportional to a weight associated with the load bearing member and the tilt piston imparts a tilt force upon the fluid proportional to a load moment associated with the load bearing member.
The means for measuring pressure within the hydraulic lift may be a number of pressure sensors with at least one pressure sensor in fluid communication with the hydraulic fluid within the lift cylinder and at least one pressure sensor in fluid communication with the hydraulic fluid within the tilt cylinder. The lift pressure sensor measures pressure of the hydraulic fluid within the lift cylinder for a period of time and creates electrical signals corresponding thereto, defining at least one pressure measurement within the lift cylinder, with the pressure within the lift cylinder being related to the lift force associated with the load bearing member. The tilt pressure sensor measures pressure of the hydraulic fluid within the tilt cylinder for a period of time and creates electrical signals corresponding thereto, defining at least one pressure measurement within the tilt cylinder, with the pressure being related to the tilt force associated with the load bearing member.
The processor includes a first sub-routine of a program stored in a memory to be operated on by the processor, determining, from a plurality of pressure measurements within the lift cylinder, the weight of the load on the hydraulic lift. The processor also includes a second subroutine of the program stored in the memory to be operated on by the processor, determining, from another plurality of pressure measurements within the tilt cylinder, an actual load moment of the load on the hydraulic lift. The processor may then use another sub-routine of the program that uses the actual load moment and the weight of the load to determine a location of a center of gravity of the load on the hydraulic lift.
The illuminated display is in data communication with the processor and produces a visual representation of the weight on the hydraulic lift. The illuminated display activates a first warning if the actual load moment is below a first predetermined load moment, activates a second warning if the actual load moment is above the first predetermined load moment and below a second predetermined load moment, and activates a third warning if the actual load moment is above the second predetermined load moment.
As stated above, the first predetermined load moment may be 80% to 100% of the rated load moment, and the second predetermined load moment may be 100% to 120% of the rated load moment. Also, the first, second, and third warnings may be colored lights. Again, the illuminated display may engage a first audio alarm if the actual load moment is above a first predetermined load moment and below a second predetermined load moment, and/or engage a second audio alarm if the actual load moment is above the second predetermined load moment.
Other features and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.